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DIAGNOSING THE CAUSES OF BIOLOGICAL IMPAIRMENT IN MOBILE BAY, ALABAMA
Citation:
ENGLE, V. D., JAN C. KURTZ, L. M. SMITH, AND J. NESTLERODE. DIAGNOSING THE CAUSES OF BIOLOGICAL IMPAIRMENT IN MOBILE BAY, ALABAMA. Presented at Alabama-Mississippi Bays and Bayous Symposium, Mobile, AL, November 27 - 29, 2006.
Description:
Mobile Bay is the fourth largest estuary in the conterminous U.S. with a watershed of more than 43,000 square miles. Biological condition in Mobile Bay has been assessed annually since 2000 through the National Coastal Assessment, a monitoring collaboration between US EPA and Alabama Department of Environmental Management (ADEM) and prior to 2000 through ADEM's ALAMAP. Several other sources of biological data are available as well from institutions such as Dauphin Island Sea Lab and Mobile Bay National Estuary Program. Benthic macroinvertebrate communities provide ideal biological indicators for estuaries because they reflect both short-term and long-term changes in environmental condition. A benthic index, developed for Gulf of Mexico estuaries, was applied to benthic macroinvertebrate community data to assess biological condition in Mobile Bay. The benthic index showed that up to 56% of Alabama estuaries were in poor biological condition from 2000 to 2004 and that Alabama estuaries received a poor ranking for biological condition every year since 2000. State environmental managers need tools to understand the potential causes of poor biological condition in order to restore the estuary to a desired environmental condition. We applied a tool developed by US EPA (CADDIS - Causal Analysis/Diagnosis Decision Information System) to evaluate the causes of poor biological condition in Mobile Bay. Potential environmental stressors that affect benthic macroinvertebrate communities include low dissolved oxygen, sediment contaminants, sediment toxicity, organic enrichment, nutrients, turbidity, sedimentation, changes in salinity, habitat alterations and disturbance. We present a case study for Mobile Bay that follows the steps recommended by CADDIS to define biological impairment, list candidate causes of that impairment, and evaluate data from the case and elsewhere to identify the most probable cause(s) of biological impairment.